Artificial line



Jan. 1, 1924' 1,479,051

F. H. BEST ARTIFICIAL LINE Filed May 14 1920 INVENTOR ATTORNEY Patented Jan. 1, 1924.

UNITED STATES PATENT: OFFICE.

FRED H. BEST, or WESTFIELD,

NEW JERSEY, ASSIGNOR '10 AMERICAN rmmrnon ARTIFICIAL LINE.

Application filed Hay 14,

To all whom it may concern:

Be it known that I, FRED H. BEST, residing at \Vestfield, in the county of Union and State of New Jersey, have invented certain Improvements in Artificial Lines, of which the following is a specification. This invention relates to artificial lines and particularly to lines of the potentiometer type. 1

It proposes to employ as the shunt resistance element, a device whose resistance per unit length is so graded, that the transmission equivalent ofthe-line varies substantially directly as the distance of movement of the contact which co-operates with this resistance, so that forreasons explained hereinafter, the scale employed to indicate thenumber of miles of actual line to which the artificial line is equivalent, maybe provided with divisions of substantially uniform lengths. The invention proposes as a resistance device of the above-defined char: acter, a wire wound on a core of graded cross section, and provided with a contact 25 which cooperates with the turns and is movable transversely with respect thereto.

A good understanding of the invention may now'be had from thefollowing description thereof having reference to the accompanying drawing showing one form and arrangement of apparatus embodying the invention in diagrammatic view.

In this drawing, reference characters AB designate the input terminals of the lineand CD the output terminals thereof. Resistances 1 and 2, of which 1 is of a special type of construction described in detail herein below, are bridged across terminals A and B, and a variable contact 3 is provided to cooperate with the resistance 1. so as to connect resistance 2 between the terminals CD. It will be observed that the'voltage CD may be adjusted, within limits, to any desired fraction of AB, from a maximum when contact 3 is at the upper terminal 4 of resistance 1, to a minimum when the same is at the lower terminal 5 thereof. v

For any position of contact 3 the length of actual line to which the artificial line is equivalent depends upon the ratio of the voltage CD to AB. This follows from the fact well known in the telephone art, that when a wave of voltage E travels along a. uniform a variable portion thereof in series with the' the resistance 1 is of 1920. smrm. 381,480.

therefore E, E r 'f whence p E L a log C E:

In the present case E =voltage AB and E, voltage CD. The voltage E may be taken asa constant. The lengthof actual line L, therefore, which is simulated by the device of my invention is a logarithmic or exponential function of the voltage CD, and consequently, likewise of the resistance included between contact?) and the terminal 6 of resistance 2. The latter resistance is of such value relatively to resistance 1 that the transmission loss in the line is the same as that of a cable having a length of, say, 10 miles, although any other length may be chosen, this value bein used herein only for sake of illustration. 9 simulate a cable of 10 miles, the contact 3 is placed at the terminal 5 of resistance 1 and to simulate a cable of less length, the contact is moved upwardly on the resistance, to include a greater portion. thereof between terminals D. Because of the inverse logarithmic relation between the volta e CD and thenumber of miles simulated, t e resistance included between 3 and 6, as the contact 3 is moved to terminal 4, has to be increased in accordance with an exponential function ofthe miles simulated. This means that when the form ofa slide-wire,

the length of resistance wire per unit length of cable simulated increases as contact 3 approaches terminal 4. The present invention proposes to. construct the resistance 1 of a wire wound on a tapered core, the taper of the core being such that when the resistance is connected as in the drawing, and contact 3 is moved longitudinally between at and 5,

equal distances of movement of the contactwill cause substantially equal changes in the transmission equivalent of' the line, no matter atwhat part of the resistance this movement takes place,v A scale 8 may therei fore be placed adjacent resistance 1 and the point With the resistance-constructed in the manner described, the scale divisions will i put terminals and comprising a resistance.

- be of substantially uniform length throughlll out the scale, so that equal accuracy may be attiiined in the use of the instrument, no

matter what part of the scale is being used.

' This would not be; the case if'the resistance were of the ordinary uniform slide wire type, for then the divisions close to terminal 5 would be very much smaller-than those close to terminal l, i. e., the length of the divisions would vary in a logarithmic or exponential order, The impedance of the circuit connected to terminals 'CD should be a large with respect to -that of the artificial line so 'thatthe voltage across AB remains constant as the position of contact 3 is varied. Y

' Although I have herein shown and de-l scribed only one form and arrangement of apparatus embodying the invention, it is readily understood that various changes and modifications may be made therein within the'scope of the following claims without departing from the spirit and scope of the invention,

impedance being ficial line at the corres ending adjustment 2. Anar-tificial line ving input-and outinvader put terminals and comprising an impedance connected between said input terminals, adjustable means to include any desired part thereof between the output terminals an indicator to show the adjustment of said means, and a scale for said indicator, said impedance being graduated and said scale;

being marked in uniform. divisions, so that the indication on the latter is in terms of and proportional to the length of a transmission line having the same attenuation as the artificial line at the corresponding adjustment;

3. An artificial line having input and outacross the input terminals, a movable contact to include a part oi said resistance across the output terminals, an indicator associated 4 with said contact, and a scale adjacent to said indicator with equal scale divisions marked in miles of transmission line, said resistance being graduated as an exponential function of the scale divisions so as to make the indicator-read correctly on the scale. I l An artificial line having input and output terminals and comprising a risistance coil across the input terminals, a sliding contact to include a part of said coil across the output terminals, an indicator carried by ,said contact, 'and a scale adjacentto said indicator with equal scale divisions marked in miles of transmission line, said coil being wound with turns of progressively increasing length so as to make the indicator reach 5 correctly on the scale.

5, An artificial line having input and out- 1 put terminals andcomprising an im edance across the. input terminals, a movab e memher to include a part of said impedance across the output terminals, an indicator associated with said member, and a scale adjacentto" said indicator marked in miles 'of transmission line, said im dance being graduated and said scale being marked to '"maike the indicator read correctly on the sca e,

In testimony whereof, I have signed my name to this specification this 13th day of May, 1929, I p FRED nnnsr. 

